In recent years, due to the use of micro-machine technology and microscopic processing technology, systems are being developed in which devices and means (for example pumps, valves, flow paths, sensors and the like) for performing conventional sample preparation, chemical analysis, chemical synthesis and the like are caused to be ultra-fine and integrated on a single chip (Patent Document 1). These systems are called μ-TAS (Micro Total Analysis System), bioreactor, lab-on-chips, and biochips, and much is expected of their application in the fields of medical testing and diagnosis, environmental measurement and agricultural manufacturing. In reality, as seen in gene screening, in the case where complicated steps, skilful operations, and machinery operations are necessary, a microanalysis system which is automatic, has high speed and is simple is very beneficial not only in terms of reduction in cost, required amount of sample and required time, but also in terms of the fact that it makes analysis possible in cases where time and place cannot be selected.
For each type of analysis or inspection, since quantitativeness, analysis accuracy, economic efficiency on these analysis chips are considered as important, the task at hand is to ensure a feeding system which has a simple structure and is highly reliable. A micro fluid control element which has high accuracy and excellent reliability is needed. The inventors of this invention have already proposed a suitable micro-pump system and a control method thereof (Patent Documents 2 to 4).
In the micro total analysis system aforementioned, to mix a plurality of fluids, for example, reagents and samples in a fine flow path in a chip is incorporated as a necessary step almost without exception. Conventionally, to mix two liquids at a mixing ratio of m:n, a method for adjusting flow rates of the liquids, thereby controlling the mixing ratio has been adopted while changing drive voltages of micro-pumps for feeding the respective liquids to change generated pressures. In this method, the mixing ratio of 1:1, or any ratio close to it will provide no problem. However, when the mixing ratio is high, it is necessary to lower the drive voltage of one micro-pump considerably, relative to the other, so that a problem arises that the mixing ratio can be hardly stabilized due to the pumping force of the other one. Further, when starting to feed fluids by the micro-pumps in the initial state that there are no fluids in the flow paths, the flow paths are slowly filled with the fed fluids in process of time. Therefore, the flow path resistances which are a load of the micro-pumps are slowly increased with time and as a result, the flow speeds of the fluids fed from the micro-pumps, that is, the flow rates are lowered slowly. Even if target values of the flow rates are determined and drive voltages according to them are supplied to the micro-pumps, a problem arises that the flow rates are varied from the target values due to changes in the flow path resistances. When the flow path is additionally extended downward from the joining part of the flow paths like this case, the flow rates are varied with time due to changes in the flow path resistance of the downstream flow path and liquid feeding pressure, so that it is more difficult to stabilize the mixing ratio.
To establish a highly reliable liquid feeding system having a simple constitution, it is essential to use a micro fluid control element which is highly accurate and reliable, to be able to change freely the mixing ratio aforementioned, and to be able to realize it stably, and thus development of a technology for that purpose is required.
Patent Document 1: Unexamined Japanese Patent Application Publication No. 2004-28589
Patent Document 2: Unexamined Japanese Patent Application Publication No. 2001-322099
Patent Document 3: Unexamined Japanese Patent Application Publication No. 2004-108285
Patent Document 4: Unexamined Japanese Patent Application Publication No. 2004-270537